Orthograde degeneration studies have outlined major ascending and descending projections of forebrain structures in reptiles. However, very little is known about the internal organization of the reptilian forebrain. The proposed research will determine the normal ultrastructure of three structures in the forebrain of snakes and turtles and use experimental electron microscopic techniques to establish the synaptic pattern of major afferents within each structure. Nucleus sphericus is an amygdaloid structure associated with the vomeronasal organs. The distribution of degenerating axon terminals in nucleus sphericus will be determined following lesions of the accessory olfactory bulb, contralateral nucleus sphericus, and of focal lesions of ipsilateral nucleus sphericus. The distribution of degenerating axon terminals in each area and layer of cerebral cortex will be determined following lesions of the thalamus and of various cortical areas. The anterior dorsal ventricular ridge is a subcortical structure which receives afferents from thalamic auditory and visual nuclei. The distribution of degenerating axon terminals in anterior dorsal ventricular ridge will be determined following thalamic and cortical lesions. BIBLIOGRAPHIC REFERENCES: Ulinski, P. S. 1977. Tectal efferents in the banded water snake, Natrix sipedon, Journal of Comparative Neurology, in press. Ulinski, P. S. 1977. Intrinsic organization of snake medial cortex: An electron microscopic and Golgi study, Journal of Morphology, in press.